Extending mobile communications network coverage and increasing a number of devices a mobile communications network can serve is an important aspect of the design and deployment of such networks. Recently, the use of relay nodes and or nodes with reduced functionality compared to an infrastructure equipment such as for example base stations have been promoted as means to achieve both increased coverage by extending the range of base stations, and increased capacity by defining an increased number of smaller cells. In a downlink (transmission from base station to mobile user device) of a communications system, conventional relaying commonly involves a signal transmitted from a base station being repeated by one or more relays of a relay chain until it is received by an intended user device. Similarly, in the uplink (transmission from the mobile user device to base station) the user device would transmit a signal to a relay and the signal would be repeated by one or more relay nodes in a relay chain until it is received by the base station. In this conventional approach, the downlink and uplink signals received and transmitted by the user device will be transmitted from and received at a same relay and or infrastructure equipment and so the uplink and downlink may be said to be coupled.
However, more recently decoupled uplink and downlink communication networks have been proposed in order to increase coverage and capacity. Decoupled uplink and downlink operation may occur for example when uplink only relays are utilised and or uplink and downlink signals are transmitted from and received at different relay nodes and or different infrastructure equipment. For instance, a user device may transmit an uplink signal to a nearby relay but receive its downlink signal directly from a base station, thus the communications paths of the uplink and downlink signals are different. This scenario can lead to increased coverage provided by the base station and may occur due to the greater transmission power of a base station compared to a user device. For example, due to power constraints, a mobile user device may only be able to transmit to a nearby relay whereas the higher transmission power associated with the base station will allow the downlink signal to be transmitted with sufficient power that it can be received directly by the mobile user device.
Although the use of decoupled uplink and downlink communications may provide additional coverage and flexibility to a communications network, a number of problems are presented. For instance, the timing of downlink signals whose transmission time is defined with respect to a transmission of an associated uplink signal may no longer be able to be reliably known at a user device because of the variable and unpredictable propagation times between the user device and the base station due to the presence of relays for example. Communications of this nature are often termed semi-synchronous communications and the random access procedure in an LTE network is an example of such a semi-synchronous procedure. In an LTE network a user device may require uplink resources in order to send a message. If in an unconnected state, the user device may transmit a request for access to the network. In an LTE network, the request for access can be a random access preamble transmitted on a physical random access channel (PRACH). In some networks, the user device may transmit the request for access to a relay which may pass on the request to a base station or another relay, or indicate to the base station by an alternative means that a request for access has been received. The mobile device is configured to wait once the request has been sent and attempt to receive a response to the request during a predefined time period after the transmission of the request. If a response is not received within this period the mobile device may attempt to initiate a subsequent access request procedure. However, due to the variable time for the request to reach the base station via one or more relay nodes, the response to the request for access may not be transmitted by the base station within the predefined time period. Consequently, the user device may waste power by attempting to receive a response to the request when one may not be transmitted until some time into the predefined time period and/or before the end of the predefined time period and also by unnecessarily initiating a subsequent access request procedure when a response is not received before the end of the predefined time period.